Sheet feeder, feed roller system and method

ABSTRACT

A sheet feed roller system for reversing the sheet contact side of a sheet feed mechanism for an offset printing press. A traction roller is attached to a pivot shaft in the place of an idler roller. A non-traction roller is attached in the place of a drive roller. A transmission is provided having a rotary input connectable to the press for receiving rotational power from the press and having a rotary output. A variant axes drive mechanism with a first end and a second end is constructed so that the first end couples to the rotary output of the transmission. A power roller is attached and coupled to the second end of the variant axes drive mechanism and so that it pivots with the pivot shaft and remains in rotational contact with the traction roller to impart rotational power to the traction roller. The power roller and the traction roller pivot together about the pivot shaft toward and away from contact with the non-traction roller so that a sheet to be fed is engaged between the traction roller and the non-traction roller and is propelled into the printing press by rolling contact with the traction roller.

BACKGROUND OF INVENTION Field of the Invention

Rotary offset printing presses are normally designed to print on one side of a sheet of printing material such as paper or other printable sheets of feed stock. Normally the sheets of printing material are fed into the printing with a roller drive mechanism through power driven rolling contact with the side of the sheet that is not to be printed. Typically the side to be printed is face up and the side that will not be printed is face down. Also typically a power driven traction drive roller is forced into contact with the face down side to propel the sheet into the press. The power driven traction roller is secured to or formed on a gear driven rotating shaft. The sheet is held by a stop gate so that the traction roller is spinning beneath or in very light contact with the sheet. Typically, when the transfer cylinder rotates the grippers into position for grabbing a new sheet, a downward contact force is applied to the non-print side, typically the top side, of the sheet to be fed by pivoting an idler roller into close proximity to the power driven traction drive roller. The sheet to be printed is engage against the traction surface of the drive roller so that it is squeezed and rolled into the press between the idler roller and the power driven traction roller.

It is often desirable to print on two sides of the same sheets of feed stock. For two sided printing to be accomplished, either a press must be configured for complex side reversing, or the sheets must first be printed on one side and later fed through the printer faced in the opposite direction for printing on the other side. For example, in a typical offset printing press a stack of clean sheet to be printed are placed in the input or feeder area, and fed through the printing press so that one side is printed and recovered in an output stack. The press is configured for printing the second side. The stack of printed sheets is removed from the output area and place printed-side-down in the input area to be fed through the press a second time to print on the other side. Thus, when printing the second side of the sheets, the initially printed sides are faced down against a power feed traction roller and blank sides are faced up toward an idler roller. The idler roller pivots down to force the printed side against the traction roller and the sheet is propelled into the press.

SUMMARY OF INVENTION

It has been found by applicant that smearing of the first printed side often occurs when the traction drive roller feeds the sheets that have already been printed on one side. This results from the rolling traction contact with the printed side of each sheet before the ink is completely dry. It will be understood that the sheet to be fed may be paper, cardstock, envelopes, film, plastic, composite material, or any other material capable of receiving printing and unless the context or the description indicates otherwise, all such sheets to be fed shall be referred to herein as a sheet or sheets to include any possible sheets to be printed. Depending upon the type of sheet material and the type of printing ink used, it can sometimes take more than a few hours for the first side of printed sheets to dry sufficiently to avoid smearing. Some types of ink and sheet combinations may take a day or more to dry sufficiently to avoid the smearing. Applicant has found that the smearing during two sided printing is often caused by rolling traction contact between the drive roller and the first printed side of the sheet. To facilitate printing a sheet on a second side within a short time of printing the first side, a sheet feeder is provided for changing the side of the sheet that the rolling traction feed roller contacts.

In one embodiment, where there is an existing sheet feed mechanism for an offset printing press, an assembly of add-on and replacement parts is constructed to convert the structure and function of the feed mechanism to drive the sheets on the opposite side from the one driven by the existing sheet feed mechanism. In this embodiment the existing feed mechanism is of the type having a drive roller for rolling traction contact with one side of the sheet and an idler roller connected to a pivot shaft for pivoting toward and away from the drive roller. Thus, according to one embodiment, a sheet feeder includes a non-traction roller sized and constructed for replacement of the existing traction drive roller. Typically, the existing drive roller of an existing sheet feeder has at least one portion that is provided with a rolling traction surface, such as a rubber surface, another polymer surface, or another surface material having traction against sheet materials, and the existing idler roller has non-traction rolling surfaces, such as polished steel, a smooth and hard plastic, or another surface having relatively low traction against a sheet material to be printed. In an embodiment where a replacement non-traction feed roller is provided, the rolling traction surface portion of the existing drive roller may be replaced with a non-traction surface. In one alternative embodiment the entire drive roller is replaced with a roller having smooth metal rolling surfaces. In other alternative embodiments, the traction surface portions of the existing drive roller may be replaced or otherwise converted to a non-traction surface. For example, and existing traction roller may have a traction coating, a traction sleeve, or cover forming a traction surface. The traction surface may be covered with a non-traction cylinder surface (such as a hard smooth tubular steel, tubular plastic, or a bearing), the traction surface may be removed down to the bare metal of the existing drive roller shaft so that traction is reduced, the traction surface may be removed and replaced with a non-traction cylinder surface (such as a hard smooth tubular steel, tubular plastic, or a bearing).

In one embodiment the non-traction drive roller whether a new replacement roller or the same roller converted to have a non-traction rolling surface may continue to be gear driven by the press. In such an embodiment replacing the traction surface with a non-traction surface has been found by applicant to avoid significant smearing of a previously printed side of the sheets. In another embodiment the traction drive roller might be replaced with a non-traction free rotating roller assuming that the mass is sufficiently small to permit quick acceleration when engaged against the sheet to be fed so that smearing does not result.

In one embodiment an existing idler roller for an existing sheet feeder will typically have a non-traction rolling surface. The existing idler roller is attached to a pivot shaft to pivot into and out of engagement with previously existing drive roller. In one embodiment of the invention, such an existing idler roller is either replaced with a replacement traction roller having a traction surface or the existing idler roller may be other wise converted to have a traction surface. This is essentially the reverse of the replacement or conversion of the existing drive roller to one having a non-traction surface. The replacement or converted traction roller continues to be mounted for pivoting on the pivot shaft. Thus, the positions of the traction roller and non-traction roller relative to the sheet to be fed are effectively reversed so the traction roller pivots toward and away from the non-traction roller.

In one embodiment a transmission assembly having a rotary input is provided that is constructed to be attachable to the offset printing press in a position for receiving rotational power in a given direction from the offset printing press. The transmission also has a rotary output that rotates in the same rotational direction as the rotary input. The output of the transmission is coupled to drive a power roller that in turn drives the traction roller. Note that the traction roller is now in the place of the previously existing idler roller that was not driven except by contact with the previously existing drive roller. Thus, the transmission and power roller are added to provide rotational power to the traction roller.

To allow the power roller to pivot with the traction roller while receiving rotational power from the transmission, a flexible drive shaft or an variant axes drive mechanism is provided. The flexible drive or the variant axes drive shaft will have opposite ends that both rotate in the same rotational direction. The axis variance capability of the flexible drive shaft or the variant axes drive mechanism permits the opposite ends of the drive shaft to rotate in the same direction about different axes. The positions of the rotational axes of the opposite ends can also be varied relative to one another during rotation. One of the ends of the variant drive mechanism and the rotary output of the transmission are constructed be coupled together. The other end of the variant axes mechanism is constructed to be coupled to a power roller. For convenient reference in this description the end coupled to the transmission may be referred to as the first end and the end coupled to a power roller may be referred to as the second end. The power roller is constructed to be mountable to an existing pivot shaft that forms part of the existing feed mechanism. The power roller is positioned intermediately between the transmission and the traction roller so that the power roller receives axial rotation from the transmission through the variant axes drive mechanism and is positioned in surface-to-surface rolling contact with traction rolling surface of the traction roller. The rolling surface of the power roller is held against the traction surface of the traction roller to impart rotational power from the power roller to the traction roller. Thus, the power roller is constructed with a traction surface for rolling contact with the traction surface of the traction roller that replaces the previously existing idler roller of an existing sheet feeder. The pivot shaft to which the power roller is mounted is the same pivot shaft that also pivots the idler roller into and out of contact with the non-traction surface of the drive roller. The power roller and the traction roller maintain their position relative to each other while they are pivoted and move together toward and away from the non-traction roller.

Typically the pivot shaft of an existing feeder mechanism is actuated by an existing pivot cam follower that is attached to the pivot shaft. The pivot cam follower engages an existing cam surface that rotates with or is otherwise driven by rotation of the press. Typically, this pivot cam surface is formed or otherwise attached on one end of the transfer roller so that there is a raised cam lobe positioned at a location around the transfer cylinder so that it will activate the sheet feeder when a gripper mechanism on a transfer cylinder is in a position for grabbing the next sheet to be fed into the printing press. A stop gate is also typically provided to operate in sequence with the printing press and the feeder mechanism to hold each next sheet to be fed so that it overlays the drive roller. According to one embodiment of the invention, the existing pivot cam, pivot cam follower and stop gate mechanisms remain in place. When the pivot cam follower engages the pivot cam lobe, it pivots the pivot shaft with the power roller and the traction roller attached so that the traction roller is brought into contact or into close proximity with the non-traction roller. At the same time the stop gate is dropped so that a sheet is driven into the press. The leading edge of the sheet is grabbed by the grippers on the transfer cylinder and is carried to the impression cylinder. After the sheet is grabbed by the transfer cylinder, the pivot cam lobe moves past the pivot follower and thereby drops the follower so that the pivot shaft moves back to a starting position with the traction roller held spaced a short distance away from the non-traction roller. The stop gate returns to its stop position when the trailing edge of the grabbed sheet passes the stop gate and the leading edge of the next sheet is thereby stopped at the stop gate. The next sheet is stopped overlaying the non-traction roller awaiting the next feed cycle when the traction roller is brought into contact with non-traction roller to start the feed cycle over again. The feed cycle is repeated so that multiple sheets are fed one-at-a-time into the printing press.

Thus, in one embodiment the new traction roller, or the idler roller with a new traction surface formed thereon, is driven in rotation by the new power roller. The new traction roller is moved toward and away from contact with the non-traction roller. The roller in the position of the previous idler roller becomes a traction roller and thereby engages and propels the sheet to be fed into the press through rolling traction contact on the side that is to be printed. It will be understood that in the case of a sheet that was previously printed on one side, the traction roller will engage the side opposite the previously printed side. In the case where printing occurs on the top side of the sheet to be fed, the traction roller engages the top of the sheet. Thus, when both sides of the sheet are blank the traction roller engages a blank side that then is printed. After the first side is printed it is place into the input stack face downward and the traction roller engages the remaining blank side that is then printed. The amount of time required between printing one side and then another side is reduced so that a two sided printing job can be competed quickly without waiting hours for the first printed side to dry completely.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic side view of a prior art rotary offset printing press with multiple sets of printing rollers and a sheet feed mechanism;

FIG. 2 is a partial perspective view showing a prior art sheet feeder attached to a printing press;

FIG. 3 is a schematic end view of one set of prior art printing cylinders and sheet feed mechanism in a non-feeding position;

FIG. 4 is a schematic end view of the set of printing cylinders and sheet feed mechanism of FIG. 3 in an engaged sheet feeding position;

FIG. 5 is a schematic side view of one set of printing cylinders and a sheet feeder mechanism in a non-feeding position according to one embodiment of the present invention;

FIG. 6 is a schematic side view of one set of printing cylinders and a sheet feeder mechanism in a sheet-feeding position according to one embodiment of the present invention;

FIG. 7 is a top view of a roller drive mechanism with a transmission and a variant axes drive for a sheet feeder according to one embodiment of the present invention;

FIG. 8 is a top view of a driven roller for a sheet feeder according to one embodiment of the present invention;

FIG. 9 is a top view of a free rolling roller for a sheet feeder according to one embodiment of the present invention;

FIG. 10 is a partial perspective view showing a sheet feeder according to one embodiment of the invention attached to a printing press;

FIG. 11 is a side assembly view of a variant axes drive mechanism for a sheet feeder according to one embodiment of the invention;

FIG. 12 is an end view of a coupler for a variant axes drive mechanism for a sheet feeder according to one embodiment of the invention;

FIG. 13 is an end view of a knuckle shaft sometimes called a “dog bone” shaft for a variant axes drive mechanism for a sheet feeder according to one embodiment of the invention;

FIG. 14 is a perspective view of a variant axes drive mechanism for a sheet feeder according to one embodiment of the invention;

FIG. 15 is a side view of an alternative embodiment of a variant axes positive drive mechanism having a knuckle or “dog bone” drive shaft for a sheet feeder in an aligned axis position according to one embodiment of the invention;

FIG. 16 is a side view of the alternative embodiment of a variant axes positive drive mechanism having a universal-joint drive shaft for a sheet feeder of FIG. 15 in an offset axis position according to one embodiment of the invention.

FIG. 17 is a side view of the alternative embodiment of a variant axes drive mechanism having a flexible shaft for a sheet feeder of FIG. 15 in an offset axis position according to one embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a side view of a prior art rotary offset printing press 10 with multiple sets of printing cylinders at 16 and 18. A first set 16 of printing cylinders includes a transfer cylinder 32, an impression cylinder 34, a blanket cylinder 36, and a plate cylinder 38. A sheet feed mechanism generally designated as 20 receives sheets to be printed from an input stack 12. The sheet feed mechanism 20 further includes a traction drive roller 22 and a non-traction idler roller 24. Those skilled in the art will understand that the terms “traction” roller and “non-traction” roller are not use in an absolute sense; rather, those terms are used to indicate relative traction capabilities so that a roller having a dominant traction capability, such as a roller having a rubber surface is called a traction roller and one having relatively less traction capabilities, such as a roller having a smooth steel surface, is called a non-traction roller. Each sheet to be printed 26 is fed into the printing press 10 one-sheet-at-a-time from the input stack 12. It will be noted that the face down side of the sheet to be printed 26 is designated “a” and the face up side is designated “b” to facilitate keeping track of the position of the sheet 26 as it move through the printing press 10.

Typically, the drive roller 22 receives rotary power from the press 10 as schematically indicated by rotational power arrow 28. The idler roller 24 is mounted on a pivot shaft 30 so that by appropriate timed cam operation the idler roller 24 is pivoted toward and away from the drive roller 22. In atypical arrangement the drive roller 22 has a traction rolling surface for contacting the sheet 26 and the idler roller 27 has a non-traction surface that contacts the sheet 26. There may be one or more axially spaced apart rolling traction surfaces on the drive roller 22 and correspondingly, one or more non-traction surfaces on the idler roller. The sheet 26 is held by a stop gate 27 so that it overlays the traction drive roller 22 without a significant amount of normal force against the traction surface of the drive roller 22 so that there is very little friction and therefore no significant traction is generated. In this position the sheet 26 is interposed horizontally between the drive roller 22 and the vertically spaced apart idler roller 24. When the idler roller 24 is pivoted toward the drive roller 22 the sheet 26 is pushed against the traction surface of the drive roller 22. The stop gate 27 is simultaneously moved to release the sheet 26, traction is generated between the sheet 26 and the traction surface of the drive roller 22, and the drive roller 22 propels the sheet 26 into the printing press 10. It will be understood that the sheet 26 moves from the transfer cylinder 32 to the impression cylinder 34, and between the impression cylinder and the blanket cylinder 36. The blanket cylinder 36, having received an ink image from plate cylinder 38, prints the image onto side “a” of the sheet 26. After the sheet 26 moves through one set 16 of printing cylinders, the sheet 26 may be further transferred by transfer cylinders 40 and 42 to another set 18 of printing cylinders 44, 46, 48, and 50 to have another color portion of the image printed on the same side “a”. Generally, each set of the printing cylinders 16 and 18 provides a different color portion of a combined multicolor image. The example shown in FIG. 1 is a typical cylinder arrangement for a two color printing press. It will be understood that any number of sets of printing cylinders, for printing additional color print portions of an image, may be provided without departing from the concepts discussed.

In the arrangement shown in FIG. 1, both sets of print cylinders, print onto the same side “a” to form a complete multicolor printed image on one side of the sheet 26. When the printing on side “a” is completed the sheet 26 is transferred, as by transfer cylinder 52, conveyor track 56, and delivery cylinder 58, onto an output stack 14. If the other side “b” is also to be printed, the output stack 14 of printed sheets would be inverted, so that side “b” is face up. Then the stack with the “b” face up would be moved to the position of input stack 12. Another printing run would be initiated, this time printing on side “b”. (Note that upon printing the once printed sheet 26 a second time after inverting the output stack 14, all of the “a” designations in FIG. 1 would become “b” designations and all the “b” designations would become “a” designations.) It will be understood, according to this description of a typical feeder mechanism 20, that the recently printed side “a” of sheet 26 would be subjected to the traction contact with drive roller 22 in the feeder mechanism 20.

FIG. 2 shows a partial perspective view of a prior art sheet feeder 20 attached to a printing press 10. The rotational power 27 is received from a gear 60 driven by the press 10 and engaged with a set of transmission gears 62, 64, and 66 that transmit rotation 27 t6o the drive roller 22. The idler roller 24 is connected to pivot shaft 30 through arms 68 that are fixed to the pivot shaft 30. The idler roller 24 freely rotates on bearings 70 about an axis that remains parallel to the drive roller 22 when pivoted The sheet to be printed 26 is fed between drive roller 22 and idler roller 24 in a timed relationship with rotation of the press 10, namely in a timed relationship with the rotation of grippers 72 on transfer cylinder 32. The grippers 72 are activated to grab the leading edge of the sheet in time with rotation of the press 10, as by a timed cam and cam follower in a known manner, for transfer via the transfer cylinder 32 to the impression cylinder 34 where printing takes place.

FIG. 3 shows a schematic enlarged end view of one set 16 of prior art printing cylinders 32, 34, 36, a transfer cylinder 40, and a sheet feed mechanism 20 in a non-feeding position. In this position the pivot shaft 30 moves the attached arms 68 upward so that the attached idler roller 24 is moved away from contact with the drive roller 22. The idler roller 24 is mounted through friction free bearings to the arms 68 and is provided with a non-traction rolling surface 25. The drive roller 22 has a traction rolling surface 23 and receives rotational power from the press 10 via a gear 60 on the transfer cylinder 32 that meshes with a gear 62 that in turn meshes with an intermediate gear 64 that meshes with gear 66 on the end of the drive roller 22. The sheet to be fed 26 is held by a stop gate 27 so that the sheet 26 is overlaying the drive roller 22. The stop gate 27 holds the sheet 26 until the appropriate time for the sheet 26 to be fed into the press 10.

FIG. 4 shows a schematic end view of the prior art set of printing cylinders and sheet feed mechanism of FIG. 3, in a sheet feeding position. The sheet feeder 20 is in an engaged sheet feeding position. In this sheet feeding position the idler roller 24 is pivoted so that its non-traction rolling surface 25 pushes against one side of the sheet 26, and the other side of the sheet 26 is thereby pushed against the traction surface 23 of the drive roller 22. At the same time, the stop gate 27 is dropped down or is otherwise opened. For example, the stop gate may be operated by a gate cam that operates in a known manner and is not shown. The traction surface 23 of rotating drive roller 22 engages and propels the sheet 26 into the printing press 10 where it is grabbed by grippers 72 on transfer cylinder 32. Typically, the surface speed of the rotating drive roller 22 is greater that the surface speed of the rotating transfer cylinder 32 so that with proper timing, sheet 26 only needs to be propelled for a short time sufficient to force the sheet 26 into position to be grabbed by grippers 72. The pivot shaft 30 then lifts the idler roller 24 off the sheet 26, slippage occurs at the traction surface 23, and the sheet 26 is pulled into the press 10 at the speed of the grippers 72 carried by the transfer cylinder 32. It will be noted that when the sheet 26 is carried on the transfer cylinder 34, a side of the sheet 26 that is designated as side “a” is facing inward against the transfer cylinder 32 and a side designated as side “b” is facing outward from transfer cylinder 32. When sheet 26 is transferred to grippers 74 on the impression cylinder 34, side “a” is facing outwardly and side “a” receives a printed image from blanket cylinder 36. For printing multi-color images, the sheet 26 is transferred to grippers 76 of an intermediate transfer cylinder 40 to be carried to one or more other sets of printing cylinders for printing one or more other colors, again on side “a” to complete the multicolor image.

FIG. 5 shows a schematic side view of an existing set 16 of printing cylinders 32, 34, 36, and a transfer cylinder 40, similar to those shown in FIGS. 1-4 above. A sheet feeder mechanism 80 according to one embodiment of the present invention is included in FIG. 5 and is shown in a non-feeding position. In this embodiment, a non traction roller 82 having a non-traction surface 86 is installed to replace and in the place of the existing drive roller that has been removed and is not shown in FIG. 5. In this embodiment the sheet 26 is positioned above the non-traction rolling surface 86. A traction roller 90 having a traction rolling surface 92 is attached to pivot shaft 30 through arms 68 with friction free bearings 91 to replace and in the place of the existing idler roller that has been removed and is not shown in FIG. 5. The traction roller 90 is operatively connected to a rotational power source 59, so that rotational power is provided to the traction roller 90 when it is pivoted into contact with a sheet 26 interposed between the traction roller 90 and the non-traction roller 82.

In one embodiment the power source 59 comprises a power roller 94 that is attached to pivot shaft 30 through a mount 96. The power roller 94 has a traction surface 95 that engages the traction surface of 92 of traction roller 90. The power roller 94 receives rotational power from the press through a series of gears and shafts. A transmission 100 is attached to the press and has an input gear 102 that meshes with gear 60 on the press. The transmission 100 transmits rotational power through an intermediate gear 104, and to an output gear 106 and to an offset drive 110. The offset drive 110 is coupled to the power roller 94. In the non-feed position shown, the pivot shaft 30 moves the arms 68 upward so that the traction surface 92 of traction roller 90 is moved away from a non-traction surface 86 of non-traction roller 82. The sheet to be fed 26 is held overlaying the non-traction surface 86 of non-traction roller 82 by a stop gate 27. Thus the rotational power is provided by this power source 59 to the traction roller 90 when it is pivoted into contact with the sheet 26. The stop gate 27 is moved out of the way to allow feeding of the sheet into the press 10.

It will be noted that in one embodiment input gear 102 may be the same as input gear 62. In such an embodiment the non-traction roller 82 may continue to be rotatably driven by gear 102 (or gear 62, as the case may be) meshing with gear 66 attached to the non-traction roller 82. Because surface 86 is a non-traction surface the driving of the sheet 26 continues to result primarily from rolling traction contact with traction roller 90.

FIG. 6 shows a schematic side view of the sheet feeder mechanism 80 of an embodiment similar to FIG. 5 shown in a sheet feeding position. The same set of printing cylinders 32, 34, and 36 and a transfer cylinder 40 are included. In the feeding position as shown and for the embodiment shown, the traction roller 90 is attached to pivot shaft 30 through arms 68 with friction free bearings 91. In this embodiment the power source 59 is again usefully provided by the power roller 94 as shown in a position for rolling engagement with traction roller 90. The power roller 94 has a traction surface 95 that engages the traction surface of 92 of traction roller 90. The power roller 94 receives rotational power from the press 10 through the transmission 100. The transmission input gear 104 meshes with press gear 60 and transmits rotation power through the transmission intermediate gear 104 and the output gear 106 to the output shaft 108. The output shaft 108 is coupled through an offset drive 110 to the power roller 94. In the sheet feeding position shown in FIG. 6, the pivot shaft 30 moves the arms 68 downward so that the traction surface 92 of traction roller 90 is moved toward the non-traction surface 86 of non-traction roller 82. The sheet to be fed 26 is effectively pushed by the non-traction surface 86 of the non-traction roller 82 into traction rolling contact with the traction surface 92 of traction roller 90. The stop gate 27 is simultaneously moved out of the way and the traction roller 90 propels the sheet 26 into the grippers 72 of the press 10. The sheet feeder 80 is constructed to drive the sheet 26 into the press at a speed that is faster than the surface speed of the transfer cylinder 32. The feeder 80 is periodically activated to feed the sheet 26 on a timed basis for a period of time sufficient for the grippers 72 on the transfer cylinder 32 to grab the sheet 26. The feeder 80 stops feeding the sheet 26 when or shortly after the grippers 72 grab the leading edge of sheet 26. The sheet feeder 80 disengages the sheet 26 after the initial rapid feed into the grippers 72 so that the transfer cylinder 32 carries the sheet without the sheet 26 buckling between the traction roller 90 and the grippers 72. To disengage the sheet feeder and stop feeding the sheet 26, the pivot shaft 30 raises the arms 68 and moves the traction roller 90 out of contact with the sheet 26. The feeding time or the time between engagement and disengagement of the sheet 26 is called the “dwell time.” The dwell time is set to be consistent for each sheet 26 to be fed one-sheet-at-a-time. The transfer cylinder 32 carries the sheet 26 to the impression cylinder 34 where the sheet 26 is grabbed by grippers. The sheet 26 is printed on side “a” between the impression cylinder 34 and the blanket cylinder 36.

FIG. 7 shows a top view of a one embodiment of the transmission 100, the off set drive mechanism 110, and the power roller 94 held on a mounting plate 150. The transmission 100 includes a power input gear 102 for meshing with and receiving rotational power from the press 10 (similar to the arrangement described in connection with FIG. 6 and not shown in FIG. 7). The transmission 100 includes an intermediate gear 104 that meshes with an output gear 106 to drive an output shaft 108. The offset drive mechanism 110, sometimes referred to as a variant axes drive mechanism 110, is coupled to the output shaft 108 at a first coupler 112. A movable drive shaft 111 between the first coupler 112 and a second coupler 130 that is in turn coupled to the power roller 94.

In the embodiment shown in FIG. 7, an offset drive mechanism 110 is depicted that may be referred to as a variant axes positive drive mechanism. The term “variant axes” is used to refer to the unique characteristics that permit the input and the output ends of the movable drive shaft 111 to rotate in the same direction about different axes, and to allow the positions of the different rotational axes to vary during rotation and use. The term “positive drive” is further used refer to providing substantially direct metal-to-metal rotational driving substantially without twisting flexure. For example, the positive drive capability of the depicted offset drive mechanism 110 is accomplished by the metal-to-metal driving engagement between the slots 116, 136 and the bearing surfaces 122, 142, respectively, and with the solid metal main shaft portion 118 therebetween. Such positive drive capability in addition to the variant axes capability is considered useful for purposes of various embodiments of the invention.

In this embodiment, the first coupler 112 is coaxially attached to the output shaft 108 of the transmission 100. To allow axis position variation between the first coupler 112 and the second coupler 130, a cylindrically shaped receiving socket 114 is formed in the first coupler 112. The receiving socket 114 has a slot 116 formed partially into one side. Similarly, the second coupler 130 has a cylindrically shaped receiving socket 134 with a slot 136 formed at least partially into one side. In the depiction shown the slots 116 and 136 are formed entirely through a side and partially along the depth of the cylindrical sockets 114 and 134 of couplers 112 and 130, respectively. The moveable shaft 111 comprises a main shaft portion 118 having a first boss 120 and a second boss 140 formed or attached at opposite ends of the shaft portion 118. Each boss 120 and 140 are formed with a partially spherical surface sized for slip fit reception into the coupler sockets 114 and 134 respectively. The moveable shaft 111 is sometimes referred to as a “knuckle shaft” or a “dog bone shaft” because of its shape.

A cylindrically shaped engagement bearing surface 122 is secured to the boss 120 so that the axis of symmetry of the cylindrical bearing surface 122 passes through the center 121 of the partially spherical boss 120. The bearing surface 122 is sized for metal to metal engagement with the interior edges of the slot 116. In this embodiment rotation of the coupler by shaft 108 is imparted by the slot 116 to the bearing surface 122 by direct metal-to-metal contact. The rotation is transmitted from the bearing surface 122 to the main shaft portion 118. The other partially spherical boss 140 is formed at the other end of the main shaft 118 and is also provided with a cylindrical bearing surface 142 attached to the partially spherical boss 140. The boss 140 and the receiving socket 134 are formed in the second coupler 130 and are sized for slip fit engagement. The slot 136 and the bearing surface 142 are sized for metal-to-metal engagement.

In the embodiment shown in FIG. 7, the bearing surfaces 122 and 142 comprise the exterior of rotational outer races of small diameter friction free ball bearings. In such an embodiment the metal-to-metal contact between the slots 116 and 136 and the bearing surfaces 122 and 142 comprises rolling contact. It will be understood by those skilled in the art upon reading this disclosure that in an alternative embodiment, the bearing surfaces 122 and 142 could be fixed non-rotating surfaces so that the metal to metal contact would be sliding contact without departing from certain useful aspects of the invention. For example, a smooth cylindrical head of an Allen bolt might be used. Lubrication considerations may be different for sliding contact compared to rolling contact.

Rotation of the shaft 108 and coupler 112 is transmitted through the slot 116 and bearing surface 122 into rotation of the main shaft portion 118 that in turn drives the bearing surface 142 to rotate the second coupler 130. The moveable shaft 111 can pivot continuously and to a certain degree about the partially spherical boss ends 120 and 140. The angular degree of pivoting of the moveable shaft 111 may depend upon the size differences between the diameter of the spherical bosses 120 and 140 and the diameter of the main shaft portion 118. Thus, the respective axes 113 and 131 of the first and second couplers 112 and 130 can be variably offset from one another and from the axis 119 of the shaft 118 while rotational force is transmitted therebetween.

The coupler 130 is connected through an axle 132 to the power roller 94. A traction surface 95 is formed on the power roller 94. The power roller 94 is held for rotation about axle 131 in journal bearings 158 held in a support bracket 160. The support bracket 160 is mounted to a mounting plate 150 that will be attached to the existing pivot shaft (not shown in FIG. 7, see pivot shaft 30 in FIG. 10 below) through mounting holes 152. In the embodiment shown in FIG. 7, the support bracket 160 is pivotally mounted to the mounting plate 150 through pivot blocks 154 and pivot pins 156. A lockdown screw 162 engages the bracket 160 through mounting plate 150. A compression spring 164 or other biasing means is interposed between the mounting plate 150 and the bracket 160 so that upon loosening of the lock down screw 162, the spring 164 pushes the bracket 160 away from the mounting plate 150. Thus, when the lock down screw 162 is not tightened and locked down, the power roller 94 is biased away from the plate 150 and is biased or spring loaded for rolling contact between traction surface 95 of the power roller and traction surface 92 of the traction roller 90 (not shown in FIG. 7, see FIGS. 8 and 10.) When the lock down screw 162 is tightened the power roller is pulled back from the traction roller 90. This feature allows the dwell time to be observed for setup purposes.

To set up the feeder mechanism 80, the lockdown screw 162 is tightened to compress the spring 164 and lock down the bracket 160 against the mounting plate 150. This lifts the power roller 94 away from the traction roller 90 so that the feeding dwell time can be conveniently observed and adjusted. For example, on a typical printing press the relative surface speeds of the feed rollers 90 and 84, compared to the speed of the grippers 72 on the transfer cylinder 32 are such that the traction roller 90 should engage for feeding a sheet 26 for about 1 to 1¼ revolutions, nominally 1⅛ revolutions, of the traction roller 90. The pivot cam lobe should typically pivot the traction roller 90 into engagement with the sheet 26 for this short duration. The desired feeding dwell time is a time sufficiently long to allow the grippers 72 to grab the sheet 26 yet sufficiently short to stop feeding the sheet 26 before the sheet 26 buckles between the traction rollers 90 and the transfer cylinder 32. In an embodiment where the non-traction roller 82 receives rotational power from the press 10, setting the dwell time is facilitated by locking down the power roller without having a sheet 26 interposed. The traction roller 90 will rotate only while it is in contact with the rotating non-traction roller 82 and will stop rotating when the pivot cam lifts apart the two rollers 90 and 82. Thus, the dwell may be conveniently observed and adjusted. After adjustment of the dwell time (as by appropriate positioning of the pivot cam follower) the lockdown screw 162 is loosened and the spring 164 is allowed to resiliently bias the power roller 94 against the traction roller 90. The resilience of the spring 164 or other biasing means is also useful if something thicker than one sheet 26 gets between the feed rollers 90 and 82. For example, if several sheets go through at once, the spring 164 can flex and avoid immediate damage. A sensor (not shown) might also determine when this occurs and the press 10 can be shut down or otherwise adjusted to avoid damage to other parts of the press as well.

It will be understood that the mount plate 150, the bracket 160, the power roller 94, the arms 68, and the traction roller 90 are all pivoted together as a pivoted sub-unit 81 by the pivot shaft 30 when a pivot cam lobe is contacted by a pivot follower for each revolution of the press. One sheet 26 is fed for each revolution and feeding cycle. It will also be noted that the transmission 100 will be mounted to the press 10 in a fixed relation to the gear 60 so that the transmission 100 does not pivot with the power roller 94 and the traction roller 90. Thus, the rotational power from the transmission output shaft 108 is uniquely transmitted to the power roller 94 using an offset drive 110, such as a variable axis drive mechanism 110. When the pivoted sub-unit 81 pivots relative to the transmission 100 the variable axis drive mechanism 110 permits the pivoting without binding and without interrupting the rotational power to the power roller 94 and the traction roller 90.

FIG. 8 shows a top view of a traction roller 90 for a sheet feeder 80 according to one embodiment of the present invention. The traction roller 90 may be constructed with one or more traction rolling surfaces 92 formed on a shaft 93. In the embodiment shown, the traction rolling surface 92 comprises a plurality of traction rolling surfaces 92 a-e spaced laterally along the traction roller 90 to facilitate feeding sheets 26 that might have different sizes. The traction rolling surfaces 92 (or 92 a-e) may, for example, be constructed of rubber, polymer, or another material having a significant amount of traction when rolling under pressure upon a paper sheet 26 or when rolling on another type material sheet 26. Such traction material might for example be molded concentrically around the shaft 93, or might be otherwise bonded or secured smoothly around the circumference of the shaft 93.

FIG. 9 shows a top view of a non-traction roller 82 for a sheet feeder according to one embodiment of the present invention. In the embodiment depicted, at least one reduced traction or non-traction surface 86 is formed on or otherwise secured to the traction roller shaft 84. The at least one non-traction surfaces 86 is positioned to be at least partially aligned with at least one traction surface 92 of the traction roller. In the embodiment shown, the non-traction rolling surface 86 comprises a plurality of non-traction rolling surfaces 86 a-e spaced laterally along the non-traction roller 82 to facilitate feeding sheets 26 that might have different sizes. Each of the plurality of non-traction surfaces 86 a-e is positioned to be at least partially aligned with the plurality of traction surfaces 92 a-e of the traction roller. The non-traction surfaces 86 a-e may be formed for example of smooth steel integrally machined on a metal shaft 84 for the traction roller 82 or the non-traction surfaces 86 a-e might be formed of another hard and durable material having a low coefficient of friction when contacting paper or other sheet material 26. A coefficient of friction for the at least one non-traction surface 86 that is relatively lower than the coefficient of friction for the at least one traction surface 92 has been found to be a useful embodiment for certain aspects of the invention. The metal shaft 84 and the non-traction surfaces carried thereon may be driven by rotation of the press 10, as for example through a gear 88.

FIG. 10 shows a partial perspective view of a sheet feeder 80 mounted on a printing press 10 according to one embodiment of the invention. In operation according to this embodiment, there is a staging mechanism 9, such as a plurality of conveyance rollers or an inclined ramp that provides an input stack 12 of sheets 26 to the sheet feeder 80. Each sheet 26 may be delivered by the staging mechanism 9 one at a time to the sheet feeder 80. In operation of one feeding cycle, the sheet feeder 80 initially prevents any sheet 26 from progressing into the press 10 (as with a stop gate 27 shown in FIG. 5). The transmission 100 provides rotation to the offset drive 110 so that the power roller 94 rotates and in turn drives the traction roller 90. The non-traction roller 82 may also be rotated by the press, but the traction force between the non-traction surface 86 and the sheet 26 is insufficient to move the sheet 26. When the grippers 72 are rotated with the transfer cylinder 32 and the sheet 26 is aligned with the grippers 72, the pivot shaft 30 will be actuated to move the traction roller 90 toward the non-traction roller 82. The traction roller 90 is still engaged with the power roller 94 so that it is rotating at a surface speed greater than the surface speed of the transfer cylinder. The traction surface 92 of the traction roller 90 engages the sheet 26 between the traction surface 92 of the traction roller 90 and the non-traction surface 86 of the non-traction roller 82. The rolling surface speed of the traction roller 90 and the non-traction roller 82 are matched and the matched surface speed of the rollers 82 and 90 exceeds the speed of the grippers 72 so the sheet 26 is propelled against the opened grippers 72. The grippers 72 are actuated to close and grab the leading edge of the sheet 26. The pivot shaft 30 is then actuated to lift the traction roller 82 out of contact with the sheet 26 and vertically spaced apart from the non-traction roller. The stop gate 27 moves up to stop the next sheet 26 overlaying the non-traction roller 82 in a position awaiting the next sheet feeding cycle. The feeding cycle is repeated for a desired number of printing cycles.

The dwell time of the pivot shaft 30 is set so that the sheet 26 is fed completely against the grippers 72 as the grippers grab the sheet; but the sheet is released by the feeder mechanism 80 before the sheet 26 buckles against the grippers 72. For example, in some printing presses a sufficient dwell time is equivalent to about one to one and one-fourth rotations of the traction roller 82. This will depend upon various aspects of the mechanism such as the relative diameters of the power roller 94, the traction roller 82, the transfer cylinder, and also the gear ratio of the transmission 100.

FIG. 11 shows a side assembly view of a variant axes positive drive mechanism 110 for a sheet feeder according to one embodiment of the invention. A first coupler 112 is attached coaxially and for rotation with an output shaft 108. A cylindrical hole or socket 114 formed in an opposite end of the coupler 112. A groove or a slot 116 is formed extending from the socket 114 toward the exterior of the coupler 112. A second coupler 130 is attached coaxially with a drive shaft 132. A socket or a socket 134 is formed in the second coupler 130. A groove or slot 136 is formed extending from the socket 134 toward the exterior of the coupler 130. A movable shaft 118 is formed having a first partially spherical shaped boss 120 on one end sized for slip fit engagement with the socket 114 of the first coupler 112 and having a second partially spherically shaped boss 140 on the other end sized for slip fit engagement with the socket 134 of the second coupler 130. A cylindrical bearing surface 122 is attached to the boss 120 and a cylindrical bearing surface 142 is attached to the boss 140. According to one embodiment, the bearing surface 122 may be formed by securing a friction free bearing 170 to the boss 120 with a fastener 172. For example, the friction free bearing 170 may be a ball bearing having a cylindrical exterior race or a roller bearing having a cylindrical exterior race. The cylindrical exterior of the bearing 170 and the slot 116 are sized for rolling contact engagement. Similarly, according to one embodiment, the bearing surface 142 may be formed by securing a friction free bearing 180 to the boss 140 with a fastener 182. For example, the friction free bearing 180 may be a ball bearing having a cylindrical exterior race or a roller bearing having a cylindrical exterior race. The cylindrical exterior of the bearing 180 and the slot 136 are sized for rolling contact engagement

FIG. 12 shows an example end view of the coupler 112 with a socket 114 and a slot 116 for the variant axes positive drive mechanism 110 shown in FIG. 11.

FIG. 13 shows an example end view of the boss 120 with a bearing 170 secured to the boss 120 with a fastener 172 along an axis 174 for the variant axes positive drive mechanism 110 shown in FIG. 11. A similar construction may be used for the boss 140. A similar construction may be used for the coupler 130.

FIG. 14 shows a perspective view of one embodiment of an assembled variant axes positive drive mechanism 110 of FIGS. 10-13, for a sheet feeder. In this assembled depiction it will be noted that the axis 113 of the coupler 112 is at a different angle than the axis 119 of the shaft 118. The axis 119 of the shaft 118 is at a different angle from the axis 131 of the coupler 130.

FIGS. 15 and 16 show side views, each with the same components differently positioned, of an alternative embodiment of a variant axes positive drive mechanism comprising a U-Joint 200. FIG. 15 shows the U-joint 200 in an aligned axis position. FIG. 16 shows the variant axes positive drive U-Joint 200 in an offset or angled position. The U-joint 200 includes a first connectable to a coupler portion 190. the first coupler 190 is coaxially aligned along axis 113 and sized and constructed for coupling to the output shaft 108 of the transmission 100 (shaft 108 and transmission 100 not shown in FIGS. 15 and 16, see FIG. 7). Rotation is transmitted through the coupler and a dual action pivot connection 191 to intermediate shaft portion 192. Rotation is transmitted from the intermediate shaft 192 to a second coupler 194 coaxially aligned along axis 193. The second coupler 194 receives rotation from the intermediate shaft 192 through a dual action pivot connection 195 and conveys the rotation along axis 131. The second coupler 194 is sized and constructed to be attachable to the drive shaft 132 that in turn rotates the power roller 94. (The drive shaft 132 and the power roller 94 are not shown in FIGS. 15 and 16, see FIG. 7.) The axes of rotation 113 and 131 at either end of the variant axes positive drive may vary during rotation

FIG. 17 is a side view of the alternative embodiment of a variant axes drive mechanism 210 having a flexible shaft 212 connecting between a first coupler 214 and a second coupler 216 in offset axis positions according to one embodiment of the invention. For example the construction might include a flexible metal spring steel coil 218 surrounded by a flexible polymer casing or tubing 220. The flexible tubing 220 might be reinforced with high tensile strength fibers for additional integrity and durability. During rotation, the axis of rotation at either end of the variant axes drive mechanism 210 may vary during rotation. Particularly the axis of rotation of the first and second couplers 214 and 216 may vary during rotation. Although, the spring steel coil has a certain amount of twisting rigidity and the casing or tubing 220 might be reinforced, the variant axes mechanism 210 might still have a limited amount of twisting flexure so that it might not be considered a positive drive. In some embodiments this alternative variant drive could be useful with out departing from certain features of the invention

Alternatives and Equivalents

In one alternative embodiment, if the non-traction roller that replaces the drive roller has a sufficiently small mass, the drive gear mechanism might be removed so that the replacement non-traction roller effectively becomes an idler roller.

Those skilled in the art might consider other offset positive drives or variant axes positive drive mechanisms could also be useful to provide an offset drive mechanism for certain purposes of the invention. One example of such another variant axes positive drive is a U-Joint shown in FIGS. 15 and 16.

Those skilled in the art might consider other offset drive mechanisms, other than the specifically a positive drive mechanisms disclosed in some of the embodiments of the present invention, might be useful for certain purposes and application. One example of a variant axes flexible drive is shown in FIG. 17. 

1. A replacement sheet feeder for changing the rolling contact traction side of a sheet to be fed in an existing sheet feed mechanism for an existing offset printing press of the type having a drive roller for driving rolling traction contact with one side of the sheet to be fed and an existing idler roller pivotable about an existing pivot shaft toward and away from the drive roller, the replacement sheet feeder comprising: a non-traction roller sized and constructed for installation in place of the existing drive roller; a traction roller sized and constructed for installation in place of the existing idler roller; and a traction roller power source operatively installed to provide rotation to the traction roller during pivoting so that the traction roller receives rotational power when it contacts a sheet to be fed on a side of the sheet to be fed opposite from the non-traction roller.
 2. The sheet feeder of claim 1, wherein the power source comprises: a transmission attachable to the existing offset printing press having a rotary input in a position for receiving rotational power in a given direction from the offset printing press, the transmission having a rotary output; a variant axes drive mechanism having first and second ends that rotate in the same rotational direction about first and second axes that are variable during rotation, the first end constructed to be coupled to the rotary output of the transmission; a power roller coupled to the second end of the variant axes drive mechanism, the power roller mountable to the existing pivot shaft so that it is positioned in rotational contact with the traction roller when the traction roller is installed in place of the existing idler roller to impart rotational power from the power roller to the traction roller, wherein the installed traction roller is pivotable toward and away from contact with the installed non-traction roller to thereby contact a sheet to be fed between the traction roller and the non-traction roller to thereby propel the sheet to be fed into the press through rolling traction contact on the traction roller side of the sheet to be fed.
 3. The sheet feeder of claim 2 wherein the variant axes drive mechanism comprises a variant axes positive drive.
 4. The sheet feeder of claim 3 wherein the variant axes positive drive comprises a knuckle shaft.
 5. The sheet feeder of claim 4 wherein the variant axes positive drive comprises a first coupler having a first socket with a first slot; a second coupler having a second socket and a second slot, a knuckle shaft having a first boss at one end of the knuckle shaft for slip fit engagement in the first socket and a first bearing surface projecting from the first boss for engagement in the first slot and having a second boss at another end of the knuckle shaft for slip fit engagement in the second socket and a second bearing surface projecting from the second boss for engagement in the second slot, wherein the first and second bosses pivot relative the first and second couplers while the bearings surfaces engage against the first and second slots to transmit rotational power through the knuckle shaft.
 6. The sheet feeder of claim 4 wherein the variant axes positive drive comprises: a U-joint having a first and second coupler on either end.
 7. The sheet feeder of claim 4 wherein the variant axes drive mechanism comprises a flexible drive shaft.
 8. The sheet feeder of claim 7 wherein the flexible drive shaft comprises: a coil metal spring encased in polymeric tubing; a first coupler formed at one end of the flexible shaft; a second coupler formed at another end of the flexible shaft, so that the first and second couplers are rotatable about variable axes through flexure of the coiled spring and polymeric tubing.
 9. The sheet feeder of claim 2 wherein the variant axes drive mechanism comprises a variant axes positive drive.
 10. The sheet feeder of claim 1 wherein the non-traction roller comprises at least one non-traction rolling surface formed on a metal shaft.
 11. The sheet feeder of claim 10 wherein the at least one non-traction rolling surface formed on a metal non-traction shaft comprises at least one smooth cylindrical metal surface formed coaxially along a portion of the metal.
 12. The sheet feeder of claim 1 wherein the traction roller comprises at least one traction rolling surface formed on a metal traction shaft.
 13. The sheet feeder of claim 12 wherein the traction rolling surface formed on a metal comprises at least one cylindrically shaped polymeric surface coaxially attached along a portion of the metal shaft.
 14. The sheet feeder of claim 2 wherein the power roller comprises a rotatable shaft having a polymeric traction surface formed thereon, the rotatable shaft mounted through bracket and journal bearings to a mounting plate in a position with the power roller parallel to the traction roller, wherein the mounting plate is attachable to the existing pivot shaft adjacent to the so that the power roller remains engaged with the traction roller when the traction roller is pivoted on the pivot shaft.
 15. The sheet feeder of claim 14 further comprising: a pivot connection between the journalled bracket rotatably holding the power roller and the mounting plate; a basing device interposed between the mounting plate and the journalled bracket operatively connected to bias the bracket and thereby to bias the power roller into rolling contact with the traction roller; and a lockdown device connecting between the bracket and the mounting plate having a locked down position holding the bracket so that the power roller is pulled away from the traction roller against the biasing device and having a release position allowing the biasing device to bias the power roller into rolling contact with traction roller.
 16. A sheet feed roller system for inverting the rolling contact side of a sheet feed mechanism for an offset printing press of the type including a drive roller operatively coupled to the offset printing press through a rotary power receiving mechanism for receiving rotational power in a given direction to rotate the drive roller, an idler roller mounted above the drive roller on a pivot shaft, and the pivot shaft operatively connected for timed alternating pivoting of the idler roller downward toward the drive roller and upward away from the drive roller so that a sheet to be fed into the press when placed overlaying the drive roller can be pushed down by the pivoted idler roller against a top side of the sheet so that a bottom side contacts against the drive roller so that the sheet to be fed is caused to be linearly propelled into the press by rolling contact with the drive roller on the bottom side of the sheet to be fed, the sheet feed roller system for inverting the rolling contact side comprising: a non-traction roller installed in place of the drive roller in a position below a sheet to be fed into the printing press; a traction roller installed on the pivot shaft in place of the idler roller for alternating pivoting toward and away from the non-traction roller; and a traction roller power source operatively connected to provide rotation to the traction roller during pivoting so that the traction roller is rotating when it is pivoted into contact with a sheet to be fed on the top side of the sheet to be fed opposite from the non-traction roller below the sheet to be fed.
 17. The sheet feed system of claim 16 wherein the traction roller power source comprises: a transmission having a rotary input positioned for receiving rotational power from the printing press and having a rotary power output; a variant axes positive drive mechanism having a first end and a second end, the first end constructed for coupling to the rotary power output of the transmission; a power roller constructed to be coupled to the second end of the variant axes drive mechanism and mountable to the pivot shaft in rotational contact with the traction roller to impart rotational power from the power roller to the traction roller and so that the power roller and the traction roller pivot together about the pivot shaft toward and away from contact with the non-traction roller so that non-traction roller receives rotational power when contacting the sheet to be fed and the sheet to be fed is propelled into the press by rolling contact with the traction roller.
 18. A sheet feeder for a printing press of the type for printing on one side of a sheet, the sheet feeder comprising: a non-traction roller installed in a position below that a staging position of sheet to be fed into the printing press, wherein the non-traction roller is adjacent to a side of the sheet that is not the side to be printed; a traction roller installed on a pivot shaft parallel to and spaced vertically above the non-traction roller and above the staging position of a sheet to be fed, wherein the pivot shaft is actuated by the press for alternating pivoting the traction roller toward and away from the non-traction roller and for contacting the side of the sheet that is the side to be printed; a transmission having a rotary input positioned for receiving rotational power from the press and having a rotary output rotated in response to rotation of the rotary input; a variant axes positive drive mechanism having a first end and a second end, the first end coupled to the rotary output of the transmission; a power roller having a rolling traction surface, the power roller coupled to the second end of the variant axes drive mechanism and mounted to the pivot shaft so that the rolling traction surface is in rolling contact with the traction roller to impart rotational power from the power roller to the traction roller and so that the power roller and the traction roller pivot together about the pivot shaft toward and away from the non-traction roller so that the sheet is propelled with rolling contact on the traction roller on top of the side of the sheet that is the side to be printed.
 19. A method for changing the rolling contact traction side of a sheet to be fed in an existing sheet feed mechanism for an existing offset printing press of the type having a drive roller for driving rolling traction contact with one side of the sheet to be fed and an existing idler roller pivotable about an existing pivot shaft toward and away from the drive roller, the replacement sheet feeder comprising: removing and existing drive roller and installing a non-traction roller in place of the removed existing drive roller; removing an existing idler roller and installing a traction roller in place of the removed existing idler roller; and installing a power source for the traction roller operatively connected to the press and the traction roller to provide rotation to the traction roller during pivoting so that the traction roller receives rotational power when it contacts a sheet to be fed on a side of the sheet to be fed opposite from the non-traction roller.
 20. The method of claim 19, wherein the installing the power source for the traction roller comprises: installing a transmission attached to the existing offset printing press, the transmission having a rotary input in a position for receiving rotational power from the offset printing press and the transmission having a rotary output; installing a variant axes drive mechanism having first and second ends that rotate in the same rotational direction about first and second axes that are variable during rotation, the first end constructed to be coupled to the rotary output of the transmission; installing a power roller coupled to the second end of the variant axes drive mechanism, the power roller mounted to the existing pivot shaft so that it is positioned in rotational contact with the traction roller when the traction roller is installed in place of the existing idler roller to impart rotational power from the power roller to the traction roller, wherein the installed traction roller is pivotable toward and away from contact with the installed non-traction roller to thereby contact a sheet to be fed between the traction roller and the non-traction roller to thereby propel the sheet to be fed into the press through rolling traction contact on the traction roller side of the sheet to be fed. 